90 attempts are made and only one third are successful. Multiply the attempts by successes and you get 30 successful shots (90 x 1/3= 30).
The z-score is given by:
z=(x-mean)/s.d
the z-score giving us P(0.95)=1.96 and -1.96
thus;
-1.96=(x-1500)/300
-588=x-1500
x=-588+1500
x=912
also:
1.96=(x-1500)/300
588=x-1500
x=588+1500
x=2,088
therefore the sample size of the student picked will be given by:
2,088-912
=1,176
